Good ideas! I had some similar thoughts..
5k: Maybe the rose in the glass, so it has the shape of that? It sort of reminds me of what the Captain America medal looked like, but reversed. (Would love it to be Gaston themed, but I'm not holding my breath - LOL, I would DIE of happiness if it was though!)
10k: Agree, will be the rose. Maybe a red ribbon to reflect the rose.
Half: Yellow stone. Blue or Yellow ribbon.
Glass Slipper: Yellow shading for sure, maybe a red or yellow ribbon.
I associate the following colors to Beauty and the Beast: Blue, Yellow and Red. Blue for her dress, yellow for the ball gown, and red for the rose and gaston's shirt. So i'm assuming the race shirts will be those colors, along with the ribbons.
I'm also wrong all of the time, too. So .... yeah.